S. Shahangian and L. P. Hager disclose in The Journal of Biological Chemistry, Vol. 256, 12 (1981) 6034, how chloroperoxidase from Caldariomyces fumago is used to first oxidize chlorite into chlorine dioxide, which chlorine dioxide may subsequently be dismutated to form chloride, oxygen and chlorate.
There are several drawbacks to said process. Apparently, the degradation of chlorite by chloroperoxidase results for the most part in chlorine dioxide which is an undesired product. It is true that said chlorine dioxide is partially converted into chloride at a later stage, but this reaction also sees the formation of undesired chlorate. In the end, it was found that about 43% of the chlorine bound in the chlorite was converted into chloride, while about 57% was converted into the undesired chlorate. Furthermore, the chlorite conversion proceeds most rapidly at a pH of less than 3.5. Such a low pH will be hindering to any other conversions intended to be performed simultaneously.
U.S. Pat. No. 5,302,285 discloses a process in which perchlorate-containing wastewater is subjected to microbiological treatment in a water-treatment plant (WTP) using an anaerobic and an aerobic reactor. In this process the perchlorate is reduced via chlorite to chloride in the first-stage anaerobic reactor using a bacterium named HAP1. Incidentally, it should be noted that this bacterium is capable of reducing chlorite to chloride enzymatically under anaerobic conditions. However, the reaction scheme in FIG. 4 of this reference indicates that the reduction of chlorite to chloride also requires a reductor. This shows that the enzyme responsible is a reductase. The reductor, e.g., hydrogen or formic acid, may also be provided by other bacteria. Also, during the reaction acids are formed which have to be neutralized, since HAP1 has optimum effectiveness in the pH range of 6.5 to 8.0.
DE-A-2,123,093 discloses a process for converting chlorine oxides with the aid of bacteria from activated sludge. This is achieved by feeding the effluent stream to be purified with a composition including many readily oxidizable compounds (reductors) and ensuring that the oxygen required for oxidation is present in a less than stoichiometric amount during anaerobic breakdown. This shows that said bacteria contain a reductase. The rate of conversion is very low. The presence of a dismutase is neither mentioned nor suggested.
NL-A-7,408,898 discloses how chlorate- or perchlorate-containing wastewater is purified anaerobically using microorganisms of the strain Vibrio dechloraticans Cusnesova B-1168, in the presence of readily oxidizable substances. The presence of a dismutase is neither mentioned nor suggested.
The invention now provides an improved process which substantially obviates the aforementioned drawbacks of the prior art.